Really interesting one this. I had something similar a few years back, standing in the garden in Hampshire just after midnight and noticed this object sitting completely still above the treeline at the bottom of the field. No sound at all, which is the thing that stuck with me most. Aircraft always make some noise don't they, even helicopters you can hear from a fair distance.
Did yours have any lights on it? And roughly how long was it there before it moved or disappeared? That bit always seems to be the detail that separates the more unusual reports from things like drones or lanterns.
Also worth noting what direction you were facing and the time if you remember it. There are a couple of databases where people log sightings by location and sometimes you get clusters that line up and thats when it gets properly interesting.